The problem began in the mid-20th century when the hazardous chemical pesticide DDT was used by virtually everyone and killed off a generation of eagles. DDT was ultimately banned in the U.S. in the 1970s, when the eagles were listed as endangered.

For nearly a decade, that first breeding pair to set up in northern New Hampshire in 1989 was the only active nest, but around the turn of the century we started to see the population trend move quickly upward.

By 2008, when the number of eagles in the state had jumped to 59 from 42 the year before, the bald eagles were removed from the state’s endangered list and placed on the threatened list, where they remain today.

The biggest rise in the eagle population happened last year. In 2014, there were 67 eagles.

Now, there are about 45 known territorial pairs in New Hampshire, about 90 individuals.

“I’m aware right now of two new nest sites that weren’t counted last year, where the birds are building now in various places in the state. So we’ll probably get to 50 [pairs] this year, maybe a little bit more,” Martin said.

There wasn’t much difference between the mid-winter count in 2015 of 90 and this year’s count of 89, but Martin says it might as well count as growth because of how the weather has played a part these two years. In 2015, it was exceedingly cold, freezing most of the state’s large water bodies, which the eagles flock to for food. In cold years like that, the birds head to the southeast, closer to the coastline and closer to the concentration of monitoring volunteers, making it more likely for them to be spotted. This year was the complete opposite, with a very warm winter, ensuring the birds are more spread out and harder to find. So, according to Martin, the fact that birders counted just as many eagles in 2016 is a very good sign.

At 79 years old, Dawn Stavros of Canterbury wakes up early one day in early February each year to drive out to a known eagle hotspot and walk along a prescribed route, writing down how many bald eagles she spots and taking note of their likely age — immature eagles have brown heads — and what kind of prey the birds are taking.

“We go out and we have our own route. There are a team of us. In the Lakes Region, I think there are about 10 or 12 teams,” Stavros said.

Stavros has been doing this longer than anyone, since the mid-winter surveys began 36 years ago, and she hasn’t missed a single year.

In fact, she used to monitor the eagles weekly for the entire winter, just for fun.

“I used to go out every Tuesday morning from the first week of December to the first week of March along the riverways, particularly Merrimack,” Stavros said.

She remembers when she first started getting involved as an amateur bird-watcher and how excited she was when the first pair of eagles to create an active nest in New Hampshire since 1949 returned to the last known nest site — the exact same tree along Lake Umbagog — in 1989.

Though Stavros and others like her aren’t getting paid for their vigilance, she takes great pride in her work.

“We had to help protect the habitat and in order to do that we had to know where the birds were that were using nest sites,” Stavros said. “There were lots of victories. There were also disappointments.”

Disappointments include certain land development projects that failed to protect habitat, Stavros said, though she noted that landowners are generally on board when it comes to helping our national bird return from the brink of extinction.

Wildlife biologist Michael Marchand with New Hampshire Fish and Game says these volunteers are the eyes and ears of the state and conservationists working to monitor and manage the bald eagle population. Without them, Marchand says, the state wouldn’t be able to conduct an effective mid-winter survey.

“We don’t have the resources to be everywhere at once,” Marchand said.

But the volunteers not only help do much of the actual monitoring work, they also help the state obtain federal grants to pay for it, by getting included in a 35 percent state match.

“Volunteer hours are a source of that match. The volunteers are valued essentially as employees and that money gets applied as the match towards the grant,” Marchand said.

The survey and other bald eagle restoration efforts are spearheaded by the New Hampshire Audubon Society, which the Fish and Game department contracts for its services.

At the Audubon, raptor biologist Chris Martin coordinates with his company of 90-odd spies deployed for the mid-winter survey and in general.

“[I’m] all the time on the phone and Internet talking to them about what they’re seeing and suggesting to them ways that they might fine tune what they’re observing,” he said.

And throughout the year, he works with about 45 volunteers who check on eagle nests to see if the birds are producing young.

If it weren’t for the volunteers, certain efforts to protect eagle habitat from land development, wouldn’t be as successful.

Stavros agrees.

“I just feel that it’s a very important thing that we have done and we are still doing. It’s not over with yet,” Stavros said.

Martin says their efforts will continue until New Hampshire reaches “carrying capacity” for the eagles. Maine, which is eight times the size of New Hampshire, has more than 700 bald eagle pairs, so he thinks it wouldn’t be unreasonable to expect about 100 bald eagle pairs in the Granite State down the road.